What is the difference between GNOME, KDE, XFCE, and LXDE?

WEBINAR:On-Demand

In Linux, there are so many choices, and this includes
the desktop environments and window managers. Four of the most
popular desktop environments in Linux are GNOME, KDE, XFCE, and
LXDE. All four offer sophisticated point-and-click graphical user
interfaces (GUI) which are on par with the desktop environments
found in Windows and Mac OS X. When you ask different people which
of these four is best, you will likely get many different answers.
So which is the best between GNOME, KDE, XFCE, and
LXDE?